PROJECT SUMMARY Resective neurosurgery is essential for treating a range of neurologic conditions such as epilepsy and brain tumors. For some patients, whose lesion is close to cortical language areas, postoperative expressive or receptive language deficit is a major and feared postoperative complication. Much effort is devoted to identifying the cortical language regions, and relating such localization to the patient?s lesion. Noninvasive mapping of cortical language function, especially for the vulnerable patient population who cannot tolerate awake craniotomy, fMRI or TMS, is an important unmet need. The investigators? long-term objective is to develop an inexpensive, convenient, high resolution scalp tripolar electroencephalography (tEEG) recording system and algorithms used to localize and map cortical function. tEEG will provide an adjunctive, noninvasive approach to surgical mapping procedures, fMRI and TMS that may not be available for children and other patient populations. Novel scalp tEEG suppresses physiologic electrical artifacts related to patient movement and cranial muscles, and artifacts related to other extraneous electrical signals to enable recording of very focal brain signals with high fidelity, which is critical for functional cortical mapping. tEEG localizes gamma activity with spatial resolution similar to that of ECoG, thus providing a quality of extracranial recording that approximates intracranial EEG. Denser tEEG, as proposed, will further increase the spatial resolution. The Phase I objective is to test the feasibility of using novel tEEG scalp recording for noninvasive functional transcranial anatomic lateralization of dominant language hemisphere and localization of cortical expressive and receptive language regions in pediatric patients with epilepsy. The following specific aims are designed to achieve the Phase I objective. Aim 1: Adapt the tEEG platform to a form that is suitable for fast, reliable, and higher spatial application in the clinical testing. Signal fidelity will be analyzed to ensure the system?s efficacy and fit. Aim 2: Record scalp tEEG during a linguistic naming task in pediatric patients with epilepsy, and test whether regions of significant event-related gamma activity correspond to the dominant language hemisphere and the receptive (temporo-parietal) or expressive (frontal) areas during the appropriate phases of the task. The patients will have already undergone language mapping by traditional approaches and will be verified to the language regions identified by tEEG.